A light emitting diode (LED) device, which is a kind of a compound semiconductor, is a device that emits light due to an applied voltage. An LED device has a small size, a long life, and high efficiency of conversion of electric energy to light energy. Accordingly, LED illuminating apparatuses using LED devices are gradually replacing incandescent lights and fluorescent lamps.
In an LED illuminating apparatus, it is important to maintain a constant quantity of light regardless of variation in a root mean square (RMS) value of an input voltage in order to maintain a constant light intensity. Here, electric power that determines the quantity of light of an LED illuminating apparatus is proportional to the product of an RMS value (Vrms) of an applied voltage, and an RMS value (Irms) of currents flowing through a closed circuit.
Meanwhile, a resistance component of a closed circuit formed in an existing LED illuminating apparatus is constant regardless of an RMS value of an applied voltage. As a result, when the RMS value of the applied voltage varies, the RMS value of currents flowing through the closed circuit varies, having a positive relationship with the RMS value of the applied voltage.
Accordingly, in the existing LED illuminating apparatus, when the applied voltage is unstable, stability of power of the LED illuminating apparatus is significantly lowered, thereby stability of the quantity of light is lowered, and thereby uniformity of light intensity is lowered.